Acoustic treatment



March 18, 1930. c, RQSENBLATT 1,751,249

AUGUST 10 TREATMENT Filed June 23, 192-7 5000s wan 00,9 TING INVENTOR: JZYU/P/f 6. FGSE/VBLFT];

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ATTORN EYL Patented 18, 1930 MAURICE C. BOSEHIBLATT, OF PHILADELPHIA, PENNSYLVANIA aoous'rrc zrnmrmmfr Application filed June 28,

This invention relates to acoustic treatments.

Among the objects. of the invention are; to provide amethod for increasing the sound absorbing efliciency of acoustic treatments;

toprovide a method for regulating and con trolling the sound absorbin efliciency of acoustic'treatments; to provi e an additional step'in methods of treating surfaces acoustically to increase the absorption of an area subjected to the step; to provide a method of improving the sound absorptive factor of acoustic treatments without adversely affecting the superficial visual aspect thereof;

to provide an acoustic treatment susceptible to cleaning and washing but with a relatively high coeflicient of sound absorption; to provide an improved acoustic treatment generally, and many other objects and advantages as will be more apparent as the description (45 which an absorbent material such as felt, for instance, has an imposed membrane pasted or cemented to it, the membrane followsgenerally. the contour of the rough surface of 4 the felt, and when the membrane is painted proceeds. k

The invention consists in the provision of a multiplicity of minute pores or openings in the outer surface of the acoustic treatment;

and, further, to the utilization of the porosity thus effected with acoustic materials and others, to form a novel acoustic treatment.

In general there are two practical methods or treatments for securing the absor tion of impinged sound waves, or a more or ess limited proportion thereof, in use in the art. That known as the non-contact membrane type, in which a membrane is stretched in spaced relation to a concealed la er of absorbent material, and which is rat or expensive and retpiires skilled workers; and the contact niem rane type, in which the covering membrane is-in contact with the concealed absorbent element. This latter type 0 is more fre uently used owingito the rela-.

tively less skilled workers necessary, and also because of the'trend toward texture finishes on the surfaces of walls and ceilings. With the contact membrane acoustic treatment, in

or otherwise coated, the sugerficial aspect -be treated. Circumstances, of course,

1927. Serial No. 201,021.

.of architectural interior finishes.

In treating a given room or auditorium for acoustic deficiencies, the ceiling is usually. the first point of attack, and if treatment of the ceiling alone does not provide the desired amount of absorption, then the walls may also alter the order of treatment, but in general the painted or coated contact membrane type of acoustic treatment upon a ceiling is fa rly eflicient as to its sound absorbin' efficiency, and is also rather pleasin to t e esthetic senses. It is to be noted, owever, that in any case the exposed membrane is painted or coated in order to make the treatment acceptable from an ornamental standpoint. Unfortunatel this coatin effects a sharp reduction in t e efliciency o the treatment as a whole. This is for the reason that the coating, be it thin plaster, or whatever else may be used fills in the pores of the membrane and forms a skin which is more or less reflective of sound may paint, either with or without oil,

waves incident thereon. The more reflective the surface of the coating the lower the ab"- sorptive efficiency of the treatment.

Much effort and expense have been' expended in an effort to find a coating material which provides a good finish, but which has such porosity as to permit the penetration of sound waves to the absorbing material beneath or behind it. So far as known this has not beeneffectively accomplished in the coating itself.

The invention herein, contemplates the tion is of particular value in connection with acoustic material other than felt, where perchance the porosity of the material is not as great as it may be made by this invention.

In the accompanying drawings, V

Fig. 1, represents a plan of an acoustic material or treatment, in which the stippled portion re resents an area containing a multiplicity 0 minute artificial pores enhancing the absor tion of the area, and the portion bounded y the circle indicates a slightly I magnified area,

Fig. 2, represents a detailed perspective of a form of acoustic treatment susceptible to improvement of the absorptive value by the invention herein,

Fig. 3, represents a fragmentary section on a greatly magnified scale of an acoustic treatment as shown in Fig. 2, with the minute artificial pores of the invention formed in the outer surface and penetrating to the main sound absorbing element,

Fig. 4, represents a side elevation of a fragment of a commercial composition board of limited sound absorb'in power, and

Fig. 5, represents a si' e elevation of the same on a greatly magnified scale, showing the formation of the multiplicity of artificial minute pores in dotted lines in the surface thereof;

By the term acoustic material is meant material having certain characteristics rendering it available for use in the solution of acoustic problems. The usual requisite is that it have the capacity to absorb more than a minimum of percentage of incident sound waves, When such material, either alone, or in combination with other materials, is applied to the structure of a building,

' thereby correcting an acoustical defect therein, it is known as an acoustical treatment.

As noted the invention herein is applicable to the material and to the treatment.

A given portion of an acoustical treatment, such as 10, may be one in which it is desirable to increase the sound absorbing efliciency of a part only, as 11. According to the invention, therefore, this latter area may be? filled with'a multiplicity of minute artificial pores 18, formed in the exposed surface of the treatment. While the minute pores of this invention may be utilized in connection with any form or type of acoustical treatment, substantially, yet it is of particular value when the treatment has a reflective and non-absorbent coating or layer, or a plurality thereof, such as is almost always present, and which invariably reduces the sound absorbing efficiency of the treatment. In' constructing or forming acoustic treatments, it is usually necessary to use one or more non-absorbing layers, such as layers of paste,'or glue, aint, etc., and although such ayers are ma e as thin as possible for the purposes intended, yet they do effect a sharp reduction of the sound absorption of the. treatment. In the drawings there is illustrated an acoustic treatment having an initial a'bsortion of value, but which absorption may e materially increased by the invention herein. A

The treatment comprises an inner layer of sound absorbing material 12, such for instance as felt or composition material, to which a relatively thin leveling layer of felt 13 may be joined by a layer of paste or glue 14. This leveling layer is not essentiahof course, but it is helpful in securing a smooth external finishnfor the treatment. Upon the leveling layer 13, a membrane 15- may be placed and joined to the leveling element by a layer of paste or glue 16.- A coating 17,

as of paint, enamel,thin plaster, etc., may be applied to the outer surface of the mem- 35 brane to impart an attractive finish to the treatment. The treatment just described has considerable value in the art, and forms the subject matter of Patent #1,671,208, issued May 29, 1928, to Maurice C. and Stanley H. Rosenblatt.

Although this treatment, for numerous reasons, is of value in acoustic work, yet it will be noted that there are three layers in the treatment which are reflective and non-porous, each of which reduces the sound absorbing efiiciency of the treatment. It will be clear that under various circumstances the composition of the treatment may be varied so as to reduce-the number of non-porous layers, but even one layer effects a diminution in the absorption. Thus the final coating alone is disadvantageous from the standpoint 'of maximum absorption, although usually necessary from an ornamental standpoint. i

It is contemplated that such acoustic treat-w ments, and others, may'have a multiplicity of minute pores 18 formed mechanically in the surface thereof. Each pore 18 is of such 11o -minute area as to be visually insignificant and relatively unnoticable, and of itself to conduce but little, possibly, to the enhancement of the absorption. In the aggregate,

however, a multiplicity of the pores, provides an appreciable'pore area. I

The pores 18 each comprise a tapered or conical hole of substantially identical diameter, and they are preferably closely grouped but evenly spacedin the area. It being understood that the factor in an acoustic treatment of material contributing to the absorption of sound is int'ercommunicating pores inwhich portions of the sound waves are trapped and their energy translated into anappreciable portion of the sound energy through the intercommunicating pores of the treatment beneath the non-porous coatin It will be understood, moreover, that the e cacy of the invention herein is not dependent upon the pores alone, except as they extend into communication with sound absorbent .material, and form passages leading into incation. There are numerous fibrous compo-..

- ments after their installation.

The invention is not only applicable to treatments after attachment to structural. elements as disclosed, but is also available and highly useful to improve the sound absorptive power of acoustic materials, as a step in the finishing method or process of fabrisition boards or sheets df'materi-al, made of waste and by-products of other industries,

.and other materials, which are highly desirable for their workability, economy, etc, and which have an initial sound absorption of value, but which can be enhanced at very slight cost by the invention herein.

' Such a material is shown in Figs. land 5, and comprises. a sheet of artificial compositionmaterial, such as 20, possessed of sufficient absorption'value as to be deemed an acoustic material, but possibly only from force of necessity owing to other advantages .such. semirigid workable materials possess. These materials are usually fibrous and have series of intercommunicating pores in the structure, but owing to the processes of manufacture; the fibers are found to lie substantially flat in the board, in planes parallel, substantially, with the surfaces thereof, and as an incident to the rolling or other compression factor in forming the sheets,

present 'a compacted mass of flat lying fibers at their flat edges or flat surfaces, that is the surfaces of greatest area. If the sound Waves could penetrate with more ease into the board 20, the soundgbsorption would be greatly enhanced, as-the-matted compacted surface presents a somewhat reflective, and possibly non-porous surface precluding the transmission of sound energy beneath the surface and into the intercommunicating pores. Clearly the board is not non-p0 rous in the strict sense, but the porosity is a minimum. As shownin Fig. 5, the pores 21 extend through the congested and matted surface into the relatively softer, more absorbent material immediately beneath -the surface. As in the finishing step for the treatment, the pores are each visually insignificent, but in the aggregate provide appreciable pore area facilitating the passage of sound waveshinto the intercommunicating 'pores of the material, and in the aggregate,

remaining visually insignificent, so as to effect no substantial visual change in the aspect of the material.

forming a multiplicity of minute pores or openings 1n the coating or membrane or both, or the coating and the concealed acoustic material upon which it is superposed, it

' is preferred that mechanical means be utilized, and the .form of mechanical means that 'may be assumed varies according to the desire of the operator. It has been found that desirable results may be had by providing a manually or otherwise actuated roller, studded. with a multi licity of sharp thin points projecting pre erably radially, .and with the tips or points a ve slight distance from the surface of the r0 er. clear that subjecting the-treatment to a roll-. ing action will'cause the tips of the points to extend into the coating,'and if desired according to their length, into "the acoustic material of the treatment. It may be made -in the form of a vibrator containing numerous closely grouped points embedded in live rubber, the vibrator head may be operated, for instance by a small throw cam on a flexible shaft operated by a small high speed electric motor: Another possible form is a flat plate studded with points, with a spring and trigger arrangement to cause the plate to be depressed slightly, and then released It will be 7 by the trigger to strike the acoustical treatment. With this latter form a clock spring maybe incorporated to strike a succession of blows. Or the perforations may be made by hand with a studded hand piece.

In any case, whatever the form assumed by the piercing mechanism, and the exact structure used to attain the resut is immaterial to the present invention, the effect is the piercing of the skin coating and the membrane, and if desired, the acoustic material itself, according to the length of the pins or points used, with a multiplicity of closely grouped perforations or pores, each of itself of mlnute area, but which in the aggregate provide such porosity. as materially to increase the absorptive factor of the treatment.

The exact figures and proportions used may vary within wide limits, but it has been found, and will be cited for illustrative purposes, that a certain acoustic material such as a certain thickness of felt has an absorptive efliciency of 40%. When a coated membrane is imposed upon the felt, the efliciency may be 22%. Using points of approximately one/one hundredth of an i ch in diameter, and spaced on centersone/thirty-second of an inch apart, it is possible to provide as many as 150,000 pores in a'square foot of surface. Each poreis minute and-is practically undiscernible to the eye, but the area of the pores in the aggregate is very appreice ciable indeed. With the figures given, api proximately 13% of the area treated is pore area, through which sound waves may pass to the acoustic material behind. It is found that the efliciency of the felt, which is 40% is reduced to 22% when the reflective coating is applied. It is found that when the step of forming the pores as recited is consummated, the 18% reduction of efiiciency accounted for by the coating beconies only 13.8% when pierced, so that the net efliciency of the completely treated surface is raised to 28.2%, an appreciable and valuable increase.

Of primary importance in the use of the invention is the fact that by this method the acoustical value of materials may be regu-- lated or controlled. Thus the efliciency of the material can be increased at one place to a 'higher point than another place. For instance, assuming an auditorium requiring treatment to reduce reverberation as well as to mlmmlze d1screte echo from an offending surface, or the focusing of sound by a curved that with the method of surfacing recited, the coating material may now be a washable,

coating, such as paint, enamel, etc., and thus "enableefi'ective acoustic treatment to be ap .plied in hospitals, and similarv institutions,

sound reflective.

where the sanitation and washability of the walls is a paramount consideration.

In adapting an acoustic treatment to this latter purpose, the coating which as in any other acoustic treatment may be preformed upon the membrane, instead, of applied thereto subsequently, may be enamel which is normally water-proof, and, of course,

When the acoustic treatment in this latter case is in position, and the multiplicity of minute pores is formed in the membrane, the efficiency of the treatment is enhanced to a point where the treatment is efiicacious, but the treatment may still be washed when desired, as the apertures or' pores are of such small diameter that a.

film of water forms over each which will dry out in a short time without penetrating to the acoustic material beneath.

An important aspect of the invention is that certain acoustic materials, such as composition boards, which are easily and cheaply worked, but which have a fairly rough exterior, may be coated directly with a thin coat of plaster, and then while still moist, the multiplicity of minute pores of this invention may be formed in it before the plaster sets, to provide a fairly eflicient acoustic treatment.

The effect visually is of rather smooth plas-- ter, the' pores being fairly undiscernible, except possibly at very short range.

It is to be noted further that the step in the process recited may be an independentone in the application of acoustic. treatments. That is the process of providing the complete acoustic'treatment need not be a continuous succession of steps. There may be a perceptible time intervalrbetw'een parts of the proc-.

ess. Thus with the invention herein recited,

the problem may be the bareincrease in the efliciency in absorption, of an old acoustic treatment. The invention is perfectly available for this purpose, and by rolling in, or otherwise forming a multiplicity of minute pores in the old acoustic treatment, the efficiency of the treatment can be increased as indicated. This is an economical procedure, as it frequently saves the larger cost of addi-- tional acoustic treatment upon other exposed surfaces of the room, such as might otherwise be necessary to secure the eficiency necessary for the problem.

It will be clear that in forming the pores it is contemplated that they pass through the coating, the membrane, and the stiffer layer of paste or glue by which the membrane is caused to adhere to the backing material, if necessary.

There are a number'of fibrous, semi rigid composition materials now before the public which have value in certain forms of acoustic treatments, as they have fairly high absorptive properties, and due to their nature can be used in many places to advantage. The invention recited herein is to be considered as applicable to suchmaterials for the increase in absorption of the materials, whether coated or not, and whether carrying an imposed membrane or not. The formation of amultiplicity of minute pores in the surfaces. of such materials supplements and augments the natural porosity of the material, so that a higher absorptive efliciencyis available than the normal material can provide. Further it renders available for acoustic purposes sheet materials that would ordinarily be unavailable for such purposes by increasing the absorptive efficiency of the material to an available point.

I claim as my invention:

1. A step in an acoustic treatment process that consists in mechanically forming a multiplicity of substantially identical visually insignificant surface piercing pores in an otherwise relatively non-porous surface of acoustic material.

2. A method of treating a surface acoustically that consists in applying acoustic material to the surface, coating the exposed sur face of the materiaL'permitting the coating to at least partially dry, then mechanically forming a multiplicity of minute pores in the surface of the coating extending through the coating to communication with the material.

3. A method of forming a washable acoustic surface which consists in applying acoustic material to' a surface, or area, then applying a washable coating to the material, then mechanically forming a multiplicity of minute pores in the coating extending through the coating to communication'with the material, each pore being of such reduced diameter as to admit a portion of an impinged sound wave but to exclude liquids.

4. An acoustic process which consists in the' fabrication or application of an acoustic material having an absorbent portion comprised of series of intercommunicating pores, and having a relatively thin film or layer in juxtaposition to the absorbent portion tending to preclude the transmission of imposed soun waves into the absorbent portion, then in forming a multiplicity of minute artificial pores in the'thin layer, each pore being visually insignificant and of such depth substantally as merely to pierce the thin layer and communicate with the intercommunicating pores of the material.

y 5. An acoustic treatment for hospital walls including a layer of acoustic material, an imposed membrane, a coating of washable ma- .through to communication with the inner stratum. I a In testimony whereof, I aflix my signature.

MAURICE G. ROSENBLATT. 

